The invention relates generally to information and document archive systems which utilize electrophotoqraphic media such as "microfiche" cards to store miniaturized copies of documents, data and the like. More particularly, the invention relates to methods and apparatus useful with add on or updatable microfiche imaging systems to electronically determine which imaging areas or frames on a microfiche have been developed or otherwise are available for imaging.
Though the use of microfiche document storage has been well known and widespread for many years now, prior attempts to reliably and economically determine how much total useful area on a microfiche is available for further imaging have been largely unsuccessful. For example, it is known generally that imaged areas on a microfiche can be electronically detected by optical sensors that emit a light beam and detect the amount of light reflected or passed through the microfiche. Imaged areas, for example alphanumeric images, may be developed on the microfiche by us of darkened particles or toner which change the light or reflectivity characteristics of the electrophotographic medium.
While these techniques for detecting imaged areas on a microfiche have been previously used, they provided little or no assurance that valid frame marks were being detected. That is, optical sensors are very sensitive to dust and dirt contamination resulting in false readings by optical sensors. Furthermore, prior techniques required strict tolerances on the sensitivity of the optical sensors, as well as the physical positioning or alignment of the sensors with respect to the microfiche. Such strict tolerances substantially increase the cost of design and maintenance of the sensor apparatus. Even the slightest misalignment or skewing of the sensors can cause false readings and erroneous position indications.
Prior apparatus also did not provide an overall mapping technique so that a partially developed or updatable microfiche could be analyzed electronically for available imaging areas. Prior analysis techniques required either visual determination of available imaging areas, or time consuming frame by frame or sequential scanning to locate an available frame for the next image. Such sequential scanning is time consuming and thus costly; for all practical purposes the use of frame by frame scanning makes random or non-sequential imaging of a microfiche prohibitive.
Accordingly, the need has existed for a low-cost and efficient apparatus and method for electronically analyzing an updatable microfiche.